Coil unit, and power transmitting device, power receiving device and wireless power transmission system using the coil unit

ABSTRACT

Disclosed herein is a coil unit that includes a coil formed by spirally winding a conductive wire, a capacitor electrically connected to the coil, a magnetic member covering the coil in an axial direction of the coil, a first metal shield covering the coil with the magnetic member interposed therebetween, and a second metal shield disposed between the magnetic member and the first metal shield so as to form a space for housing the capacitor. The second metal shield includes a flat plate part facing to the magnetic member, a side wall disposed around the capacitor, and a flange part formed by bending a leading end portion of the side wall extending toward the first metal shield. The flange part is disposed so as to be thermally connected to the first metal shield.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to the structure of a coil unit suitablyused for a wireless power transmission system. The present inventionalso relates to a power transmitting device, a power receiving deviceand a wireless power transmission system using the coil unit.

Description of Related Art

A wireless power transmission technology that transmits power withoutusing a power cable or cord is now attracting attention. The wirelesspower transmission technology allows power to be transmitted from apower transmitting side to a power receiving side by wireless and isthus expected to be applied to various products such as transportequipment (electric trains, electric cars, unmanned carriers, etc.),home electric appliances, electronic devices, wireless communicationdevices, toys, and industrial equipment.

As the wireless power transmission technology, there is known a powertransmission system that utilizes a resonance phenomenon for the purposeof extending a transmission distance. The resonance phenomenon isgenerated by a resonance circuit formed by a coil connected with acapacitor.

In the above power transmission system, by integrating the coil and thecapacitor with each other, size reduction of the coil unit is attained.For example, JP 2016-103612 A discloses a coil unit in which a capacitoris disposed in a protruding support part of a shield member.

However, JP 2016-103612 A does not mention anything about exhaust ofheat generated due to current flow in the coil, and the heat generationmay lead to breakage of components, such as a coil and capacitor,constituting the coil unit.

SUMMARY

The present invention has been made in view of the above problem, andthe object thereof is to provide a coil unit capable of efficientlyradiating heat, and a power transmitting device, a power receivingdevice and a wireless power transmission system using the coil unit.

To solve the above problems, according to the present invention, thereis provided a coil unit including a coil formed by spirally winding aconductive wire, a capacitor electrically connected to the coil, amagnetic member covering the coil in an axial direction of the coil, afirst metal shield covering the coil with the magnetic member interposedtherebetween, and a second metal shield disposed between the magneticmember and the first metal shield so as to form a space for housing thecapacitor. The second metal shield includes a flat plate part facing tothe magnetic member, a side wall disposed around the capacitor, and aflange part formed by bending a leading end portion of the side wallextending toward the first metal shield. The flange part is disposed soas to be thermally connected to the first metal shield.

A power transmitting device according to the present invention includesa coil unit having the above-described features of the present inventionand an inverter circuit connected to the coil unit. According to thepresent invention, there can be provided a power transmitting devicecapable of reducing a leakage magnetic flux largely circulating a regionaway from its opposing coil while suppressing heat generation.

A power receiving device according to the present invention includes acoil unit having the above-described features of the present inventionand a rectifying circuit connected to the coil unit. According to thepresent invention, there can be provided a power receiving devicecapable of reducing a leakage magnetic flux largely circulating a regionaway from its opposing coil while suppressing heat generation.

A wireless power transmission system according to the present inventionincludes a power transmitting device that transmits power by wirelessand a power receiving device that receives the power from the powertransmitting device by wireless. At least one of the power transmittingdevice and power receiving device includes a coil unit having theabove-described features of the present invention. According to thepresent invention, there can be provided a wireless power transmissionsystem capable of reducing a leakage magnetic flux largely circulating aregion away from its opposing coil while suppressing heat generation.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of this inventionwill become more apparent by reference to the following detaileddescription of the invention taken in conjunction with the accompanyingdrawings, wherein:

FIG. 1 is a block diagram illustrating the configuration of a wirelesspower transmission system according to a preferred embodiment of thepresent invention;

FIG. 2 is a schematic cross-sectional view illustrating theconfiguration of the coil unit according to a first embodiment of thepresent invention;

FIG. 3 is a perspective view of the coil unit in a state where a resincover is detached;

FIG. 4 is a perspective view of the coil unit in a state where a resincover is attached; and

FIG. 5 is a schematic cross-sectional view illustrating theconfiguration of the coil unit according to a second embodiment of thepresent invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Preferred embodiments of the present invention will now be explained indetail with reference to the drawings.

FIG. 1 is a block diagram illustrating the configuration of a wirelesspower transmission system according to a preferred embodiment of thepresent invention.

As illustrated in FIG. 1, a wireless power transmission system 1includes a combination of a power transmitting device 2 and a powerreceiving device 3 and transmits power from the power transmittingdevice 2 to the power receiving device 3 by wireless.

The power transmitting device 2 includes a DC power supply 4, a powertransmitting circuit 5 including an inverter circuit that converts a DCvoltage supplied from the DC power supply 4 into an AC voltage of, e.g.,100 kHz, and a coil unit 10 including a power transmitting coil 6 a thatgenerates an AC magnetic flux by the AC voltage. Although the coil unit10 according to the present embodiment constitutes an LC seriesresonance circuit in which capacitors 6 b and 6 c are connected inseries respectively to both ends of the power transmitting coil 6 a, itmay constitute an LC parallel resonance circuit or an LC series-parallelresonance circuit. The number of the capacitors is not particularlylimited, and a configuration in which only the capacitor 6 b isconnected is possible.

The power receiving device 3 includes a coil unit 10 including a powerreceiving coil 7 a that receives at least a part of the AC magnetic fluxgenerated by the power transmitting coil 6 a to generate an AC voltageand a power receiving circuit 8 including a rectifying circuit thatconverts the AC voltage generated by the power receiving coil 7 a into aDC voltage. The rectifying circuit may have a smoothing function. The DCvoltage output from the power receiving device 3 is supplied to a load9. Although the coil unit 10 according to the present embodimentconstitutes an LC series resonance circuit in which capacitors 7 b and 7c are connected in series respectively to both ends of the powerreceiving coil 7 a, it may constitute an LC parallel resonance circuitor an LC series-parallel resonance circuit. The number of the capacitorsis not particularly limited, and a configuration in which only thecapacitor 7 b is connected is possible.

FIG. 2 is a schematic cross-sectional view illustrating theconfiguration of the coil unit 10 used in both the power transmittingside and power receiving side. FIGS. 3 and 4 are each a perspective viewof the coil unit 10. FIG. 3 illustrates a state where a resin cover 18is detached, and FIG. 4 illustrates a state where the resin cover 18 isattached. FIG. 2 is a schematic cross-sectional view taken along lineA-A of FIG. 4.

As illustrated in FIGS. 2 to 4, the coil unit 10 includes a coil 11formed by spirally winding a conductive wire, a capacitor 12electrically connected to the coil 11 to constitute an LC resonancecircuit, a magnetic member 13 disposed on the back side of the coil 11,a base shield (first metal shield) disposed on the back side of themagnetic member 13, and a shield box 16 disposed between the magneticmember 13 and the base shield 14 and housing the capacitor 12. The backside of the coil 11 refers to one end side in the extending direction ofa coil axis X₀ of the coil 11, which is the side opposite to a mainsurface of the coil 11 that faces a power transmission direction. Theback side of the magnetic member 13 refers to the side of the magneticmember 13 that faces away from the surface thereof opposite to the coil11.

The coil 11 corresponds to the coil 6 a or 7 a of FIG. 1. The coil 11 iswound around a resin bobbin 17 and is housed inside the resin cover 18.Although the coil 11 according to the present embodiment has a singlelayer structure, it may have a multilayer structure. Although the planarshape of the coil 11 is preferably an ellipse elongated in onedirection, an oval, or a substantially rectangular shape, it may be aperfect circle or a substantially square shape.

The capacitor 12 corresponds to the capacitors 6 b and 6 c or capacitors7 b and 7 c of FIG. 1. The capacitor 12 is packaged together with thecoil 11 to constitute a power transmitting coil unit. While thecapacitor 12 is attached to the shield box 16 in the present embodiment,but may be attached to the base shield 14. Since the capacitor 12 isdisposed on the back side of the coil 11 with the magnetic member 13 andthe shield box 16 interposed therebetween, it does not block powertransmission by the metal part (terminal electrode, internal electrode,etc.) thereof. A pair of terminals of the LC resonance circuitconstituted by the coil 11 and capacitor 12 are each connected with apower cable 19.

The magnetic member 13 is a sheet-like or plate-like member made of amagnetic material such as ferrite and is provided so as to cover theentire back surface of the coil 11. The magnetic member 13 may be anaggregate of a plurality of magnetic pieces. In the present embodiment,the magnetic member 13 is bonded to the back surface of the bobbin 17.By thus providing the magnetic member 13 on the back side of the coil11, a magnetic path for a magnetic flux ϕ interlinking the coil 11 canbe ensured, whereby power transmission efficiency can be enhanced.

The base shield 14 is a support made of metal such as copper or aluminumand having an outer dimension larger than those of the coil 11 andmagnetic member 13. The base shield 14 is provided for shielding amagnetic flux leaking to the back side of the coil 11. A heat sink 20 isprovided on the back side of the base shield 14 that is the side facingaway from the surface opposite to the shield box 16. The heat sink 20 isconstituted of a plurality of extending fins 20 a and a flat plate part20 b on which the fins 20 a are provided, and the flat plate part 20 bis connected to the back surface of the base shield 14. In a coil unitthat handles high power, heat generation amounts of the coil 11 andmagnetic member 13 become significantly large. So, by forming the backside of the base shield 14 that is the side opposite to the powertransmission direction of the coil 11 into a heat sink structure, heatradiation performance of the coil unit 10 can be enhanced. Although theheat sink 20 is formed of a separate member from the base shield 14 inthe present embodiment, the base shield 14 and the flat plate part 20 bof the heat sink 20 may be made common and integrally formed.

The shield box 16 is a substantially box-shaped metal frame provided forensuring a space for housing the capacitor 12 on the back side of thecoil 11. The shield box 16 according to the present embodiment is formedsimply by bending a single metal plate such as a copper plate or analuminum plate and has a substantially parallelepiped outer shape.Specifically, the shield box 16 has a flat plate part 16 a disposedopposite to the back surface of the magnetic member 13, a side wall 16 bextending from both end portions of the flat plate part 16 a in thewidth direction, and a flange part 16 c formed by bending inward (oroutward) the leading end portion of the side wall 16 b. A housing slot16 d for the capacitor 12 is provided on the back side of shield box 16opposite to the base shield 14. Thus, the shield box 16 according to thepresent embodiment has a planar shape elongated in one direction asviewed in the axial direction of the coil.

The flat plate part 16 a of the shield box 16 contacts the back surfaceof the magnetic member 13 directly or through an intermediate materialsuch as a thermal compound and is thermally connected to the magneticmember 13. The flange part 16 c of the shield box 16 contacts a mainsurface 14 a of the base shield 14 directly or through an intermediatematerial such as a thermal compound. With this configuration, the flatplate part 16 a of the shield box 16 (second metal shield) is thermallyconnected to the base shield 14 (first metal shield) through the sidewall 16 b and flange part 16 c. In particular, the flat part of theflange part 16 c is opposed to the main surface 14 a of the base shield14 and, thus the base shield 14 and the shield box 16 are in surfacecontact with each other, thus enhancing heat conductivity.

In the present embodiment, the outer dimension of the flat plate part 16a of the shield box 16 (second metal shield) as viewed in the directionof the coil axis X₀ is preferably equal to or smaller than the outerdimension of the magnetic member 13. That is, the profile of the flatplate part 16 a coincides with or falls within the profile of themagnetic member 13 (i.e., does not protrude from the profile of themagnetic member 13). With this configuration, a magnetic flux ϕ_(e)emitted from an end portion 13 e of the magnetic member 13 does notinterlink the flat plate part 16 a, thus making it possible to preventheat generation of the flat plate part 16 a.

As illustrated, the magnetic member 13 and the flat plate part 16 a ofthe shield box 16 may each have a flat-plate shape as a whole.Alternatively, the magnetic member 13 and the flat plate part 16 a mayeach have a shape having, at the center thereof, an openingcorresponding to an opening of the coil 11, or a shape further having aslit extending outward from the opening. Also in these cases, theprofile of the opening of the flat plate part 16 a should not protrudefrom the profile of the magnetic member 13 in order to prevent heatgeneration of the flat plate part 16 a.

As illustrated in FIG. 3, an opening 16 e is formed in a part of theside wall 16 b of the shield box 16 surrounding the capacitor 12, andthe power cable 19 connected to the coil 11 or capacitor 12 is drawnoutside the shield box 16 through the opening 16 e. The leading ends ofthe pair of power cables 19 are connected to the inverter circuit in thecase of the coil unit 10 of the power transmitting device 2 andconnected to the rectifying circuit in the case of the coil unit 10 ofthe power receiving device 3.

The opening 16 e is preferably formed at both ends of shield box 16 inthe longitudinal direction, and the power cable 19 is drawn out from oneof the two openings 16 e. In a system where power is transmitted insubstantially the horizontal direction with the coil surface verticallyerected, height reduction of the coil unit 10 can be achieved byinstalling the coil unit 10 widthwise. In this case, when the opening isformed in the side wall on one end side of the shield box 16 in theshort length direction, the height of the coil unit 10 is increased bythe power cable 19 drawn from the one end side of the shield box 16 inthe short direction. However, when the power cable 19 is drawn from oneend side of the coil unit 10 in the longitudinal direction, the heightreduction of the coil unit 10 is not hindered by the power cable 19,thus allowing e height reduction of the entire coil unit 10.

The side wall 16 b and flange part 16 c are preferably arranged in thelongitudinal direction of the shield box 16 (flat plate part 16 a). Withthis structure, the sectional area of a heat conducting path can beincreased, and an area that the shield box 16 contacts the base shield14 can be ensured as widely as possible, whereby thermal resistance canbe reduced to enhance heat radiation performance. Further, the opening16 e can be formed at the both ends of the shield box 16 in thelongitudinal direction, whereby the power cable 19 can be drawnhorizontally. Thus, as illustrated in FIG. 3, when power transmission isperformed in substantially the horizontal direction with the coilsurface erected vertically, the coil unit 10 can be installed widthwise,whereby height reduction of the coil unit 10 can be achieved.

It is preferable that the coil axis X₀ of the coil 11 extends insubstantially the horizontal direction, and that the wireless powertransmission system 1 performs power transmission in substantially thehorizontal direction. When power transmission is performed in thevertical direction with the power transmitting coil and power receivingcoil vertically facing each other, there is a fear that a state where ametal foreign matter exists on the upper surface of the coil facingupward is continued. In this case, power transmission efficiency may bedeteriorated due to existence of the metal foreign matter to disablepower transmission. However, when power transmission is performed insubstantially the horizontal direction with the coil surface verticallyerected, metal that may adhere to the vertically erected coil surfacefalls from the coil surface, making it possible to avoid deteriorationin power transmission efficiency and further to avoid heat generation ofthe metal foreign matter.

As described above, the coil unit 10 according to the present embodimentis provided with the metal shield box 16 (second metal shield) forhousing the capacitor 12. The shield box 16 has the flange part 16 cformed by bending the leading end portion of the side wall 16 bsurrounding the capacitor 12, and the flange part 16 c is thermallyconnected to a main surface of the base shield 14 (first metal shield).This allows reduction in heat resistance between the base shield 14 andthe shield box 16 to thereby enhance heat radiation performance. Thus,it is possible to efficiently radiate heat generated from the coil 11 ormagnetic member 13 while suppressing overheat of the capacitor 12.

In addition, in the coil unit 10 according to the present embodiment,the outer dimension of the shield box (second metal shield) does notprotrude from the magnetic member 13 in a plan view, so that it ispossible to prevent a magnetic flux generated from the coil 11 andemitted from the end portion of the magnetic member 13 from interlinkingthe flat plate part 16 a, thereby making it possible to suppress heatgeneration of the flat plate part 16 a associated with an eddy currentgenerated by interlinkage of the magnetic flux. Further, the shield box16 is thermally connected to the base shield 14 (first metal shield),allowing heat generated in the coil unit 10 to be radiated efficiently.

FIG. 5 is a schematic cross-sectional view illustrating theconfiguration of a coil unit according to the second embodiment of thepresent invention.

As illustrated in FIG. 5, a coil unit 10 according to the presentembodiment is featured in that it further includes a side shield 15disposed so as to cover the periphery of the coil 11. The side shield 15is integrally formed with a flat plate part 21 parallel to the baseshield 14 by bending of a single metal plate such as a copper plate oran aluminum plate. The side shield 15 may be formed of a member separatefrom the flat plate part 21. The side shield 15 is disposed spaced apartfrom the end portion 13 e of the magnetic member 13 in the Y-axisdirection, and a distance Ly (first distance) from the magnetic member13 to the side shield 15 in the Y-axis direction is larger than at least0 and preferably larger than a distance from the center of the coil 11to the innermost conductive wire closest to the center of the coil 11.This allows a leakage magnetic flux largely circulating a region awayfrom its opposing coil to be shielded while suppressing shielding of amain magnetic flux contributing to power transmission, whereby it ispossible to reduce the leakage magnetic flux while maintaining a desiredpower transmission efficiency.

The shield box 16 is provided between the magnetic member 13 and thebase shield 14 and, thus, the base shield 14 is also disposed spacedapart from the magnetic member 13 in the X-axis direction (axialdirection of the coil). That is, a distance Lx (second distance) from areference plane SS including the back surface of the magnetic member 13that faces away from the surface thereof opposite to the coil 11 to thebase shield 14 in the X-axis direction is larger than 0. The base shield14 only needs to be separated away in the X-axis direction from thereference plane SS at least in a region between the end portion 13 e ofthe magnetic member 13 and the side shield 15. With this configuration,the main magnetic flux contributing to power transmission can beprevented from being shielded by the base shield 14. Thus, it ispossible to enhance power transmission efficiency while suppressing heatgeneration of the base shield 14.

A length Lp of a part of the side shield 15 that protrudes forward fromthe magnetic member 13 in the extending direction of the coil axis X₀ ofthe coil 11 is larger than at least 0 and preferably smaller than boththe distance Ly from the end portion 13 e of the magnetic member 13 tothe side shield 15 in the Y-axis direction and the distance Lx from themagnetic member 13 to the base shield 14. The distance Lx from themagnetic member 13 to the base shield 14 is preferably smaller than thedistance Ly from the end portion 13 e of the magnetic member 13 to theside shield 15 and, more preferably, equal to or larger than 0.6 timesthe Ly and smaller than 1 time the Ly (0.6 Ly≤Lx<Ly). With thisconfiguration, the side shield 15 of a proper size can be provided at aposition properly separated from the end portion 13 e of the magneticmember 13. This allows reduction in a leakage magnetic flux largelycirculating a region away from its opposing coil while suppressingshielding of the main magnetic flux contributing to power transmission,whereby it is possible to reduce noise while maintaining a desired powertransmission efficiency. Further, not only the side shield 15, but alsothe base shield 14 can be provided at a position properly separated fromthe end portion 13 e of the magnetic member 13. Thus, it is possible tosuppress an increase in the thickness of the coil unit while suppressingheat generation of the base shield 14.

Further, in the present embodiment, the base shield 14 is provided onthe metal flat plate part 21 integrally formed with the side shield 15,and the heat sink 20 is connected to the base shield 14 through the flatplate part 21. The heat sink 20 does not contact the back surface of thebase shield 14 but is thermally connected to the base shield 14 throughthe flat plate part 21. Thus, heat generated in the coil 11 or magneticmember 13 can be transmitted to the heat sink 20 to enhance heatradiation performance. That is, the same effects as those in the firstembodiment can be obtained. Although the flat plate part 21 is formed ofa member separate from the base shield 14 in the present embodiment, theflat plate part 21 and the base shield 14 may be made common andintegrally formed.

It is apparent that the present invention is not limited to the aboveembodiments, but may be modified and changed without departing from thescope and spirit of the invention.

For example, in the above embodiments, both the power transmittingdevice 2 and power receiving device 3 use the coil unit 10 according tothe present invention; however, the present invention is not limited tothis, only one of the power transmitting device 2 and power receivingdevice may use the coil unit 10 according to the present invention.

As described above, according to the present embodiments, there isprovided a coil unit including: a coil formed by spirally winding aconductive wire; a capacitor electrically connected to the coil; amagnetic member disposed on one end side of the coil in the axialdirection of the coil; a first metal shield disposed on the side of themagnetic member that faces away from the surface thereof opposite to thecoil; and a second metal shield disposed between the magnetic member andthe first metal shield so as to form a space for housing the capacitor.The second metal shield includes a flat plate part disposed opposite tothe surface of the magnetic member that faces away from the surfacethereof opposite to the coil, a side wall disposed around the capacitor,and a flange part formed by bending the leading end portion of the sidewall extending toward the first metal shield. The flange part isdisposed so as to be thermally connected to the first metal shield.

According to the present embodiments, it is possible to efficientlyradiate heat generated in the coil unit while suppressing overheat ofthe coil and capacitor. Further, heat resistance between the first metalshield and the second metal shield can be reduced to thereby enhanceheat radiation performance.

In the present embodiments, the flange part is preferably formed bybending inward the leading end potion of the side wall. This allows sizereduction of the second metal shield to thereby reduce an installationarea of the second metal shield relative to the first metal shield.

In the present embodiments, the second metal shield is preferablydisposed so as to be thermally connected to the magnetic member. Thisallows heat generated in the coil unit to be radiated more efficiently.

In the present embodiments, it is preferable that the second metalshield has a planar shape elongated in one direction as viewed in theaxial direction of the coil and that the flange part is disposed alongthe longitudinal direction of the second metal shield. This allows heatgenerated in the coil unit to be radiated more efficiently.

In the present embodiments, an opening is preferably formed in a part ofthe side wall, through which a power cable connected to the coil orcapacitor is drawn outside. This allows a terminal of the coil unit tobe easily drawn.

In the present embodiments, it is preferable that the second metalshield has a planar shape elongated in one direction as viewed in theaxial direction of the coil, that the coil axis extends in substantiallythe horizontal direction, and that the opening is formed on one end sideof the second metal shield in the longitudinal direction thereof. Withthis configuration, the height of the coil unit can be reduced in asystem where power transmission is performed in substantially thehorizontal direction with the surface of the coil arranged substantiallyvertically. Further, the substantially vertically arranged coil surfaceprevents a metal foreign matter from adhering to the coil surface,thereby making it possible to avoid deterioration in power transmissionefficiency due to the metal foreign matter and heat generation of themetal foreign matter. The coil axis only needs to extend substantiallyhorizontally and need not extend strictly horizontally. Thus, the angleof the coil axis only needs to fall within ±10° with respect to thehorizontal axis.

In the present embodiments, the outer dimension of the first metalshield as viewed in the axial direction of the coil is preferably largerthan the outer dimension of the second metal shield. This allows heatradiation performance of the entire coil unit to be enhanced.

In the present embodiments, a heat sink is preferably provided on theside of the first metal shield that faces away from the surface thereofopposite to the second metal shield. The structure in which powertransmission is performed horizontally and in which the heat sink isprovided on the back surface of the first metal shield allowsachievement of height reduction of the coil unit, enhancement of powertransmission efficiency, and more efficient radiation of heat generatedin the coil unit.

A power transmitting device according to the present embodimentsincludes a coil unit having the above-described features of the presentembodiments and an inverter circuit connected to the coil unit.According to the present embodiments, there can be provided a powertransmitting device capable of reducing a leakage magnetic flux largelycirculating a region away from its opposing coil while suppressing heatgeneration.

A power receiving device according to the present embodiments includes acoil unit having the above-described features of the present embodimentsand a rectifying circuit connected to the coil unit. According to thepresent embodiments, there can be provided a power receiving devicecapable of reducing a leakage magnetic flux largely circulating a regionaway from its opposing coil while suppressing heat generation.

A wireless power transmission system according to the presentembodiments includes a power transmitting device that transmits power bywireless and a power receiving device that receives the power from thepower transmitting device by wireless. At least one of the powertransmitting device and power receiving device includes a coil unithaving the above-described features of the present embodiments.According to the present embodiments, there can be provided a wirelesspower transmission system capable of reducing a leakage magnetic fluxlargely circulating a region away from its opposing coil whilesuppressing heat generation.

According to the present embodiments, there can be provided a coil unitcapable of radiating heat efficiently and a power transmitting device, apower receiving device and a wireless power transmission system usingthe coil unit.

What is claimed is:
 1. A coil unit comprising: a coil formed by spirallywinding a conductive wire; a capacitor electrically connected to thecoil; a magnetic member covering the coil in an axial direction of thecoil; a first metal shield covering the coil with the magnetic memberinterposed therebetween; and a second metal shield disposed between themagnetic member and the first metal shield so as to form a space forhousing the capacitor, wherein the second metal shield includes a flatplate part facing to the magnetic member, a side wall disposed aroundthe capacitor, and a flange part formed by bending a leading end portionof the side wall extending toward the first metal shield, and whereinthe flange part is disposed so as to be thermally connected to the firstmetal shield.
 2. The coil unit as claimed in claim 1, wherein the flangepart is formed by bending inward the leading end potion of the sidewall.
 3. The coil unit as claimed in claim 1, wherein the second metalshield is disposed so as to be thermally connected to the magneticmember.
 4. The coil unit as claimed in claim 1, wherein the second metalshield has a planar shape elongated in one direction as viewed in theaxial direction of the coil and, wherein the flange part is disposedalong a longitudinal direction of the second metal shield.
 5. The coilunit as claimed in claim 1, wherein an opening is formed in a part ofthe side wall, through which a power cable connected to the coil orcapacitor is drawn outside.
 6. The coil unit as claimed in claim 5,wherein the second metal shield has a planar shape elongated in onedirection as viewed in the axial direction of the coil, wherein the coilaxis extends in substantially a horizontal direction, and wherein theopening is formed on one end side of the second metal shield in alongitudinal direction thereof.
 7. The coil unit as claimed in claim 1,wherein an outer dimension of the first metal shield as viewed in theaxial direction of the coil is larger than an outer dimension of thesecond metal shield.
 8. The coil unit as claimed in claim 1, furthercomprising a heat sink provided on a rear side of the first metal shieldopposite to a front side facing to the second metal shield.
 9. A powertransmitting device comprising: a coil unit; and an inverter circuitconnected to the coil unit, wherein the coil unit comprising: a coilformed by spirally winding a conductive wire; a capacitor electricallyconnected to the coil; a magnetic member covering the coil in an axialdirection of the coil; a first metal shield covering the coil with themagnetic member interposed therebetween; and a second metal shielddisposed between the magnetic member and the first metal shield so as toform a space for housing the capacitor, wherein the second metal shieldincludes a flat plate part facing to the magnetic member, a side walldisposed around the capacitor, and a flange part formed by bending aleading end portion of the side wall extending toward the first metalshield, and wherein the flange part is disposed so as to be thermallyconnected to the first metal shield.
 10. A power receiving devicecomprising: a coil unit; and a rectifying circuit connected to the coilunit, wherein the coil unit comprising: a coil formed by spirallywinding a conductive wire; a capacitor electrically connected to thecoil; a magnetic member covering the coil in an axial direction of thecoil; a first metal shield covering the coil with the magnetic memberinterposed therebetween; and a second metal shield disposed between themagnetic member and the first metal shield so as to form a space forhousing the capacitor, wherein the second metal shield includes a flatplate part facing to the magnetic member, a side wall disposed aroundthe capacitor, and a flange part formed by bending a leading end portionof the side wall extending toward the first metal shield, and whereinthe flange part is disposed so as to be thermally connected to the firstmetal shield.
 11. A wireless power transmission system comprising: apower transmitting device that transmits power by wireless; and a powerreceiving device that receives the power from the power transmittingdevice by wireless, wherein at least one of the power transmittingdevice and power receiving device includes a coil unit that comprises: acoil formed by spirally winding a conductive wire; a capacitorelectrically connected to the coil; a magnetic member covering the coilin an axial direction of the coil; a first metal shield covering thecoil with the magnetic member interposed therebetween; and a secondmetal shield disposed between the magnetic member and the first metalshield so as to form a space for housing the capacitor, wherein thesecond metal shield includes a flat plate part facing to the magneticmember, a side wall disposed around the capacitor, and a flange partformed by bending a leading end portion of the side wall extendingtoward the first metal shield, and wherein the flange part is disposedso as to be thermally connected to the first metal shield.